Radio receivers, or tuners, are widely used in applications requiring the reception of electromagnetic energy. Applications can include broadcast receivers such as radio and television, set top boxes for cable television, receivers in local area networks, test and measurement equipment, radar receivers, air traffic control receivers, and microwave communication links among others. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic radio waves.
The design of a receiver is one of the most complex design tasks in electrical engineering. In the current state of the art, there are many design criteria that must be considered to produce a working radio receiver. Tradeoffs in the design's performance are often utilized to achieve a given objective. There are a multitude of performance characteristics that must be considered in designing the receiver.
However, certain performance characteristics are common to all receivers. Distortion and noise are two such parameters. The process of capturing the signal creates distortion that must be accounted for in the design of the radio receiver. The distortion must either be filtered out or canceled. Once a radio signal is captured, the noise surrounding the received signal in the receiver must be considered. Radio signals are often extremely weak and if noise is present in the circuit, the signal, even though satisfactorily received, can be easily lost in this noise floor. The current state of the art in receiver design is often directed to overcoming these receiver limitations in a cost effective manner.
In an integrated radio receiver ESD discharge circuitry is typically utilized to protect the integrated circuit from static discharge. Radio signals in a receiver tend to be of small amplitude and high frequency and are therefore susceptible to distortion caused by capacitive loading by standard ESD control methods. It is therefore desirable to provide a system of ESD protection that does not interfere with the reception of the high frequency, small amplitude signals.
Inductors are utilized in a receiver to provide frequency selectivity that helps eliminate distortion and interference. Inductors are not easily integrated onto a semiconductor substrate. Spiral inductors typically used have a low Q that provides insufficient selectivity, requiring filters to be fabricated off of the integrated circuit substrate.